public class Solution617 {
    public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        if(root1 == null){
            return root2;
        }
        if(root2 == null){
            return root1;
        }
        TreeNode mergeRoot = new TreeNode(root1.val + root2.val);
        mergeRoot.left = mergeTrees(root1.left, root2.left);
        mergeRoot.right = mergeTrees(root1.right, root2.right);
        return mergeRoot;
    }
}
